Underlayer compositions for multilayer lithographic processes

ABSTRACT

Compositions suitable for forming planarizing underlayers for multilayer lithographic processes are characterized by the presence of (A) a polymer containing: (i) cyclic ether moieties, (ii) saturated polycyclic moieties, and (iii) aromatic moieties for compositions not requiring a separate crosslinker, or (B) a polymer containing: (i) saturated polycyclic moieties, and (ii) aromatic moieties for compositions requiring a separate crosslinker. The compositions provide outstanding optical, mechanical and etch selectivity properties. The compositions are especially useful in lithographic processes using radiation less than 200 nm in wavelength to configure underlying material layers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/514,212, filed Feb. 28, 2000, the disclosure of which isincorporated herein by reference.

This application is a divisional of U.S. patent application Ser. No.10/026,184 filed on Dec. 21, 2001 now U.S. Pat. No. 6,818,381, thedisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

In the microelectronics industry as well as in other industriesinvolving construction of microscopic structures (e.g. micromachines,magnetoresistive heads, etc.), there is a continued desire to reduce thesize of structural features. In the microelectronics industry, thedesire is to reduce the size of microelectronic devices and/or toprovide greater amount of circuitry for a given chip size.

Effective lithographic techniques are essential to achieving reductionof feature sizes. Lithography impacts the manufacture of microscopicstructures not only in terms of directly imaging patterns on the desiredsubstrate, but also in terms of making masks typically used in suchimaging. Typical lithographic processes involve formation of a patternedresist layer by patternwise exposing the radiation-sensitive resist toan imaging radiation. The image is subsequently developed by contactingthe exposed resist layer with a material (typically an aqueous alkalinedeveloper) to selectively remove portions of the resist layer to revealthe desired pattern. The pattern is subsequently transferred to anunderlying material by etching the material in openings of the patternedresist layer. After the transfer is complete, the remaining resist layeris then removed.

The resolution capability of lithographic processes is generally afunction of the wavelength of imaging radiation, the quality of theoptics in the exposure tool and the thickness of the imaging layer. Asthe thickness of the imaging resist layer increases, the resolutioncapability decreases. Thinning of a conventional single layer resist toimprove resolution generally results in compromise of the etchresistance of the resist which is needed to transfer the desired imageto the underlying material layer. In order to obtain the resolutionenhancement benefit of thinner imaging layers, multilayer lithographicprocesses (e.g., so-called bilayer process) have been developed. Inmultilayer lithographic processes, a so-called planarizing underlayerlayer is used intermediate between the imaging resist layer (typically asilicon-containing resist) and the underlying material layer to bepatterned by transfer from the patterned resist. The underlayer layerreceives the pattern from the patterned resist layer, and then thepatterned underlayer acts as a mask for the etching processes needed totransfer the pattern to the underlying material.

While planarizing underlayer materials exist in the art, there is acontinued desire for improved compositions especially compositionsuseful in lithographic processes using imaging radiation less than 200nm (e.g., 193 nm) in wavelength. Known underlayers for I-line and 248 nmDUV multilayer lithographic applications are typically based on Novolacor polyhydroxystyrene polymers. These materials very strongly absorb 193nm radiation, thus are not suitable for 193 nm lithographicapplications.

The planarizing underlayer compositions should be sufficiently etchableselective to the overlying photoresist (to yield a good profile in theetched underlayer) while being resistant to the etch process needed topattern the underlying material layer. Additionally, the planarizingunderlayer composition should have the desired optical characteristics(e.g., refractive index, optical density, etc.) such that the need forany additional antireflective layer is avoided. The planarizingunderlayer composition should also have physical/chemical compatibilitywith the imaging resist layer to avoid unwanted interactions which maycause footing and/or scumming.

It is also desired to reduce the number of separate ingredients in theplanarizing underlayer composition in order to enhance the economicviability of multilayer lithographic processes.

SUMMARY OF THE INVENTION

The invention encompasses novel planarizing underlayer precursorcompositions which are useful in multilayer lithographic processes.These underlayer precursor compositions provide underlayers havingoutstanding optical, mechanical and etch selectivity properties. Theinvention also encompasses lithographic structures containing theunderlayers prepared from the compositions of the invention, methods ofmaking such lithographic structures, and methods of using suchlithographic structures to pattern underlying material layers on asubstrate.

In one aspect, the invention encompasses an underlayer precursorcomposition suitable for formation of a planarizing underlayer, thecomposition comprising:

-   -   (a) a polymer containing:        -   (i) cyclic ether moieties,        -   (ii) saturated polycyclic moieties, and        -   (iii) aromatic moieties, and    -   (b) an acid generator.        The acid generator is preferably a thermally activated acid        generator. Where the underlayer is to be used with 157 nm        lithographic process, the polymer preferably further includes        fluorine moieties.

In an alternative embodiment, the invention encompasses an underlayerprecursor composition suitable for formation of a planarizingunderlayer, the composition comprising:

-   -   (a) a polymer containing:        -   (i) saturated polycyclic moieties, and        -   (ii) aromatic moieties,    -   (b) an acid generator, and    -   (c) a crosslinker.

In another aspect, the invention encompasses a lithographic structure ona substrate, the structure comprising:

-   -   (a) a planarizing layer obtained by reacting an underlayer        precursor composition of the invention,    -   (b) a radiation-sensitive imaging layer over the planarizing        layer.

In another aspect, the invention encompasses method of forming apatterned material feature on a substrate, the method comprising:

-   -   (a) providing a material layer on a substrate,    -   (b) forming a planarizing layer over the material layer, the        planarizing layer being formed by reacting an underlayer        precursor composition of the invention,    -   (c) forming a radiation-sensitive imaging layer over the        planarizing layer,    -   (d) patternwise exposing the imaging layer to radiation thereby        creating a pattern of radiation-exposed regions in the imaging        layer,    -   (e) selectively removing portions of the imaging layer and the        planarizing layer to expose portions of the material layer, and    -   (f) etching the exposed portions of the material layer, thereby        forming the patterned material feature.        The material to be patterned is preferably a conductive,        semiconductive, magnetic or insulative material.

The invention also encompasses methods of making lithographicstructures.

These and other aspects of the invention are discussed in further detailbelow.

DETAILED DESCRIPTION OF THE INVENTION

The invention encompasses novel planarizing underlayer precursorcompositions which are useful in multilayer lithographic processes. Theinvention also encompasses lithographic structures containing theunderlayers obtained from the precursor compositions of the invention,methods of making such lithographic structures and methods of using suchlithographic structures to pattern underlying material layers on asubstrate.

In a first embodiment, the planarizing underlayer precursor compositionsof the invention generally comprise:

-   -   (a) a polymer containing:        -   (i) cyclic ether moieties,        -   (ii) saturated polycyclic moieties, and        -   (iii) aromatic moieties, and    -   (b) an acid generator.

The cyclic ether moieties are preferably present in groups pending frommonomers making up at least a portion of the backbone of the polymer.Preferably, the cyclic ether moieties are pendant from acrylate monomers(e.g., an acrylate or methacrylate) as part of an ester group. Ifdesired, other components may be present in the ester group (e.g., asaturated polycyclic moiety such as shown below). Examples of cyclicether moieties are trioxane, tetrahydrofuran, oxetane, oxepane,trithiane, tetrathiane, and epoxy moieites. The cyclic ether moiety ispreferably an epoxy moiety, more preferably a glycidyl moiety.

The saturated polycyclic moieties may be present in groups pending frommonomers making up at least a portion of the backbone of the polymer ormay themselves be present as part of the polymer backbone (e.g., in thecase where a cyclic olefin monomer is used in the polymer). Thesaturated polycyclic moieties are preferably pendant from acrylatemonomers (e.g., an acrylate or methacrylate) as part of an ester group.The saturated polycyclic moieties preferably contain at least 7 carbonatoms, more preferably about 10 to 20 carbon atoms. Examples of suchmoieties are norbornyl, isonorbornyl, adamantyl, etc.

The aromatic moieties are preferably present in groups pending frommonomers making up at least a portion of the backbone of the polymer.The aromatic moieties may be non-fused aromatic rings (e.g., benzyl,phenyl or phenol groups) or fused aromatics such as anthracene.Generally, non-fused aromatic rings are preferred aromatic moieties. Thearomatic moieties are preferably pendant from an ethylenic monomer(e.g., where styrene or hydroxystyrene are used in the polymer).

The relative mole ratio of moieties (i)-(iii) in the polymer ispreferably selected to achieve the desired combination of optical andetch properties in the resulting underlayer. Preferably, the polymercontains about 10-50 mole % of (i) cyclic ether moieties, about 20-60mole % of (ii) saturated polycyclic moieties, and about 20-60 mole % of(iii) aromatic moieties where the mole % are based on the total moles ofmoieties (i)-(iii) in the polymer.

Some examples of suitable polymers for the first embodiment are shownbelow:

where x, y, and z represent the relative quantities of each monomer.Generally, terpolymers such as shown in structures III and IV are thepreferred polymers for use in the invention.

In an alternative embodiment, the underlayer precursor composition maycomprise:

-   -   (a) a polymer containing:        -   (i) saturated polycyclic moieties, and        -   (ii) aromatic moieties,    -   (b) an acid generator, and    -   (c) a crosslinker.

The relative mole ratio of moieties (i)-(ii) in the polymer ispreferably selected to achieve the desired combination of optical andetch properties in the resulting underlayer. Preferably, the polymercontains about 40-70 mole % of (i) saturated polycyclic moieties, andabout 30-60 mole % of (ii) aromatic moieties where the mole % are basedon the total moles of moieties (i)-(ii) in the polymer. The polymers ofthe alternative embodiment preferably contain hydroxyl functionality toa sufficient extent to promote reaction with the crosslinker.

Some examples of suitable polymers for the alternative embodiment areshown below:

where x, y, and z represent the relative quantities of each monomer.

The compositions of the invention preferably produce underlayers havingan extinction coefficient (k) of about 0.2-0.8, more preferably about0.3-0.5 and a refractive index (n) of about 1.6-2.0, more preferablyabout 1.65-1.8. For cyclic olefin or acrylate-based imaging layers, a kvalue of 0.6 to 0.8 reduces standing waves for contact or trenchapplications.

If the underlayer is to be used in a multilayer lithographic processusing 157 nm imaging radiation, the polymer preferably contains afluorine component. The fluorine may be present as a pentafluoroarylgroup (e.g., as perfluorostyrene), a trifluoromethyl group (e.g., as atrifluoromethyacrylate) or in another form compatible with the otherconstituents of the planarizing layer composition and with the synthesistechniques used to form the polymer.

The underlayer compositions of the invention are preferablysubstantially free of silicon, especially where the imaging layer is asilicon-containing resist.

The polymers of the invention preferably have a weight average molecularweight, before any crosslinking reaction, of at least about 1000, morepreferably a weight average molecular weight of about 5000-50000.

The acid generator is preferably an acid generator compound thatliberates acid upon thermal treatment. A variety of known thermal acidgenerators are suitably employed such as e.g.2,4,4,6-tetrabromocyclohexadienone, benzoin tosylate, 2-nitrobenzyltosylate and other alkyl esters of organic sulfonic acids. Compoundsthat generate a sulfonic acid upon activation are generally suitable.Other suitable thermally activated acid generators are described in U.S.Pat. Nos. 5,886,102 and 5,939,236; the disclosures of these two patentsare incorporated herein by reference.

If desired, a radiation-sensitive acid generator may be employed as analternative to a thermally activated acid generator or in combinationwith a thermally activated acid generator. Examples of suitableradiation-sensitive acid generators are described in U.S. Pat. Nos.5,886,102 and 5,939,236. Other radiation-sensitive acid generators knownin the resist art may also be used as long as they are compatible withthe other components of the planarizing underlayer composition. Where aradiation-sensitive acid generator is used, the cure (crosslinking)temperature of the composition may be reduced by application ofappropriate radiation to induce acid generation which in turn catalyzesthe crosslinking reaction. Even if a radiation-sensitive acid generatoris used, it is preferred to thermally treat the composition toaccelerate the crosslinking process (e.g., for wafers in a productionline).

If desired in the first embodiment and definitely in the alternativeembodiment, the compositions of the invention may contain a separatecrosslinking component that can be reacted with the underlayer polymerin a manner which is catalyzed by generated acid and/or by heating.Generally, the crosslinking component used in the underlayercompositions of the invention may be any suitable crosslinking agentknown in the negative photoresist art which is otherwise compatible withthe other selected components of the composition. The crosslinkingagents preferably act to crosslink the polymer component in the presenceof a generated acid. Preferred crosslinking agents are glycolurilcompounds such as tetramethoxymethyl glycoluril,methylpropyltetramethoxymethyl glycoluril, andmethylpropyltetramethoxymethyl glycoluril, available under thePOWDERLINK trademark from American Cyanamid Company. Other possiblecrosslinking agents include: 2,6-bis(hydroxymethyl)-p-cresol, compoundshaving the following structures:

including their analogs and derivatives, such as those found in JapaneseLaid-Open Patent Application (Kokai) No. 1-293339, as well as etherifiedamino resins, for example methylated or butylated melamine resins(N-methoxymethyl- or N-butoxymethyl-melamine respectively) ormethylated/butylated glycolurils, for example as can be found inCanadian Patent No. 1 204 547. Other crosslinking agents such asbis-epoxies or bis-phenols (e.g., bisphenol-A) may also be used.Combinations of crosslinking agents may be used.

The planarizing underlayer compositions of the invention preferablycontain (on a solids basis) (i) about 50-98 wt. % of the polymer, morepreferably about 70-80 wt. %, (ii) about 0-50 wt. % of crosslinkingcomponent, for the alternative embodiment: preferably about 3-25%, morepreferably about 5-25 wt. %, and (iii) about 1-20 wt. % acid generator,more preferably about 1-15 wt. %.

The planarizing underlayer compositions of the invention may be used incombination with any desired resist material in the forming of alithographic structure. Preferably, the resist is imageable withultraviolet radiation (e.g. <400 nm wavelength) or with electron beamradiation. Examples of suitable resist materials are described in U.S.Pat. Nos. 5,861,231; 5,962,184; and 6,037,097, the disclosures of whichare incorporated herein by reference. A preferred resists for bilayerapplications using 193 nm radiation are disclosed in U.S. patentapplication Ser. No. 09/514,212, filed Feb. 28, 2000, the disclosure ofwhich is incorporated herein by reference.

The planarizing underlayer compositions of the invention will typicallycontain a solvent prior to their application to the desired substrate.The solvent may be any solvent conventionally used with resists whichotherwise does not have any excessively adverse impact on theperformance of the underlayer composition. Preferred solvents arepropylene glycol monomethyl ether acetate or cyclohexanone. The amountof solvent in the composition for application to a substrate ispreferably sufficient to achieve a solids content of about 8-20 wt. %.Higher solids content formulations will generally yield thicker coatinglayers. The compositions of the invention may further contain minoramounts of auxiliary components (e.g., surfactants, dyes, etc.) as maybe known in the art.

The planarizing underlayer compositions of the invention can be preparedby combining the polymer, acid generator, and any other desiredingredients using conventional methods. The compositions of theinvention advantageously may be formed into planarizing underlayers on asubstrate by spin-coating followed by baking to achieve crosslinking andsolvent removal. The baking is preferably conducted at about 250° C. orless, more preferably about 170°-230° C. The baking time may be varieddepending on the layer thickness and bake temperature. A typical time at215° C. would be about two minutes.

The thickness of the planarizing underlayer composition of the inventionmay be varied depending on the underlying topography and the intendedetch protocol (for etching the material layer to be patterned). Thethickness is preferably about 0.3-5.0 μm.

The compositions of the invention are especially useful for lithographicprocesses used in the manufacture of integrated circuits onsemiconductor substrates. The compositions are especially useful forlithographic processes using 193 nm or shorter wavelength UV imagingradiation.

Semiconductor lithographic applications generally involve transfer of apattern to a layer of material on the semiconductor substrate. Thematerial layer of the semiconductor substrate may be a metal conductorlayer, a ceramic insulator layer, a semiconductor layer or othermaterial depending on the stage of the manufacture process and thedesired material set for the end product. The composition of theinvention is preferably applied directly over the material layer to bepatterned, preferably by spin-coating. The composition is then baked toremove solvent and cure (crosslink) the composition. Aradiation-sensitive resist layer can then be applied (directly orindirectly) over the cured planarizing underlayer composition of theinvention. The resist is preferably a silicon-containing resistimageable with the desired wavelength of radiation.

Typically, the solvent-containing resist composition is applied usingspin coating or other technique. The substrate with the resist coatingis then preferably heated (pre-exposure baked) to remove the solvent andimprove the coherence of the resist layer. The thickness of the appliedlayer is preferably as thin as possible provided that the thickness ispreferably substantially uniform and that the resist layer be sufficientto withstand subsequent processing (typically reactive ion etching) totransfer the lithographic pattern to the planarizing underlayer. Thepre-exposure bake step is preferably conducted for about 10 seconds to15 minutes, more preferably about 15 seconds to one minute. Thepre-exposure bake temperature may vary depending on the glass transitiontemperature of the resist.

After solvent removal, the resist layer is then patternwise-exposed tothe desired radiation (e.g. 193 nm ultraviolet radiation). Wherescanning particle beams such as electron beam are used, patternwiseexposure may be achieved by scanning the beam across the substrate andselectively applying the beam in the desired pattern. More typically,where wavelike radiation forms such as 193 nm ultraviolet radiation, thepatternwise exposure is conducted through a mask which is placed overthe resist layer. For 193 nm UV radiation, the total exposure energy ispreferably about 100 millijoules/cm² or less, more preferably about 50millijoules/cm² or less (e.g. 15-30 millijoules/cm²).

After the desired patternwise exposure, the resist layer is typicallybaked to further complete the acid-catalyzed reaction and to enhance thecontrast of the exposed pattern. The post-exposure bake is preferablyconducted at about 60-175° C., more preferably about 90-160° C. Thepost-exposure bake is preferably conducted for about 30 seconds to 5minutes.

After post-exposure bake, the resist structure with the desired patternis obtained (developed) by contacting the resist layer with an alkalinesolution which selectively dissolves the areas of the resist which wereexposed to radiation. Preferred alkaline solutions (developers) areaqueous solutions of tetramethyl ammonium hydroxide. The resultinglithographic structure on the substrate is then typically dried toremove any remaining developer solvent.

The pattern from the resist structure may then be transferred to theexposed portions of the planarizing underlayer of the invention byreactive ion etching or other suitable etch techniques known in the art.

After the opening of the planarizing underlayer of the invention, theunderlying material layer to be patterned may then be etched using anetchant appropriate to the material layer composition. Once the desiredpattern transfer has taken place, any remaining underlayer and resistmay be removed using conventional stripping techniques.

Thus, the compositions of the invention and resulting lithographicstructures can be used to create patterned material layer structuressuch as metal wiring lines, holes for contacts or vias, insulationsections (e.g., damascene trenches or shallow trench isolation),trenches for capacitor structures, etc. as might be used in the designof integrated circuit devices.

Examples of lithographic processes where the composition of theinvention may be useful are disclosed in U.S. Pat. Nos. 4,855,017;5,362,663; 5,429,710; 5,562,801; 5,618,751; 5,744,376; 5,801,094;5,821,469 and 5,948,570, the disclosures of which patents areincorporated herein by reference. Other examples of pattern transferprocesses are described in Chapters 12 and 13 of “SemiconductorLithography, Principles, Practices, and Materials” by Wayne Moreau,Plenum Press, (1988), the disclosure of which is incorporated herein byreference. It should be understood that the invention is not limited toany specific lithography technique or device structure.

EXAMPLE 1 Synthesis of Structure III Polymer

Styrene 78.03 g, 0.74 mole), glycidylmethacrylate (159.82 g, 1.12 mole),isobornylmethacrylate (138.75 g, 0.62 mole), azobisisobutyronitrile(AIBN) catalyst (14.25 g, 3.5% of total moles of monomers) and 1128 g oftetrahydrofuran (THF) (25% wt-wt conc.) were combined in a three liter3-neck round bottom flask equipped with condenser, thermometer, anitrogen inlet and a magnetic stirrer bar. The reaction mixture wasstirred at room temperature and bubbled with N₂ flow for 1 hour priorturning the heating mantle on. The reaction was conducted for 18 hoursat 67-70° C. with a blanket N₂ flow. Then, the reaction solution wascooled to room temperature, diluted with equal volume of THF and addeddropwise to stirring hexane (1:10). The slurry was stirred overnightbefore filtration. Solid was air dried for five hours and re-dissolvedin THF (15% wt-wt) and reprecipitated in hexane (1:10). The solid wascollected by filtration and air dried for five hours. Final drying wascarried out in a vacuum oven at 60° C. overnight. The yield was 83%.

EXAMPLE 2

The above polymer was formulated into a planarizing underlayercomposition by combining with 4.75 wt. % of an acid generatordi-(t-butyl)iodonium perfluorobutane sulfonate (PFBuS) in PMA solvent. Asolution was coated to 5000 Å and baked at 225° C. for 2 minutes priorto resist coating with a silicon-containing resist described incopending application Ser. No. 09/514,212. Profiles with no foot or scumwere achieved at 125 nm equal lines and spaces using a 0.60 NA 193nmstepper.

1. A method of forming a patterned material feature on a substrate, saidmethod comprising: (a) providing a material layer on a substrate, (b)forming a planarizing layer over said material layer, said planarizinglayer being formed by reacting a planarizing underlayer composition,said underlayer composition comprising a polymer containing: (i) poxymoieties, (ii) saturated polycyclic hydrocarbon moieties, (iii) aromaticmoieties, and (iv) fluorine-containing moieties, and an acid generator,(c) forming a radiation-sensitive imaging layer over said planarizinglayer, (d) patternwise exposing said imaging layer to radiation therebycreating a pattern of radiation-exposed regions in said imaging layer,(e) selectively removing portions of said imaging layer and planarizinglayer to expose portions of said material layer, and (f) etching saidexposed portions of said material layer, thereby forming said patternedmaterial feature.
 2. The method of claim 1 further comprising: (g)removing any remaining portions of said imaging layer and saidplanarizing layer from material layer.
 3. The method of claim 1 whereinsaid radiation is ultraviolet radiation having a wavelength less than200 nm.
 4. The structure of claim 1 wherein said imaging layer is asilicon-containing resist.
 5. The method of claim 1 wherein saidmaterial layer is selected from the group consisting of dielectric,metals, and semiconductors.